1. Field of the Invention
This application pertains to a clean air cabinet. More particularly, this application pertains to a clean air cabinet including novel construction for improving compactness, manufacture and performance.
2. Background of the Invention
In the prior art, clean air cabinets are widely used in laboratory environments. Biological safety cabinets are a unique segment of clean air equipment used to protect product and operator from contamination with bacteria, virus, chemicals and toxic particulates. Performance and design parameters of biological safety cabinets were originated by numerous medical agencies with a very prominent role being played by the National Institutes of Health, Bethesda, Md. A combined effort of government agencies, academia, cabinet manufacturers and The National Sanitation Foundation (Ann Arbor, Mich.) established a Standard 49 for Class II Biohazard Cabinetry in 1976. Class II cabinets are identified as, Type A, Type B1, Type B2 and Type B3. The invention described herein is a Class II, Type B1 Biological Safety Cabinet. An example of a Class II, Type B1 Biological Safety Cabinet is the Labgard 420.TM. manufactured and sold by NuAire, Inc. of Plymouth, Minn. Such a cabinet is described in NuAire, Inc. brochure entitled LABGARD 420. On the second page of said brochure an airflow schematic is presented showing airflow through the cabinet. As indicated, room air is drawn into a grill located on the front of the cabinet work area. The air flows downward through a high efficiency particulate air (HEPA) filter located below the work surface drawn by a blower creating a vacuum in the blower compartment. The air then pressurized by the blower flows upward in a side duct on the outside of the work zone to a plenum located above the work zone; then flows downward through a second HEPA filter (or a grill) into the work zone providing clean air for the work in process. Most of the downflow air is exhausted through a dedicated duct passing to the atmosphere after passing through a HEPA filter. It is important to note that in the Class II Type B1 Cabinet the air exhausted from the work zone is not recycled and that this condition coupled with the manner in which the air is exhausted from the back of the work area provides a 100% exhaust zone for work performed in the back half of the work tray. A further characterization of the Class II, Type B1 cabinet is that the airflow through the cabinet passes through the HEPA filters that are in series in contrast to Class II, Type A cabinets in which the HEPA filters are in parallel, i.e. the supply and exhaust filters receive pressurized airflow from a common plenum.
In the manufacture of clean air cabinets, cost control is very important. Also, it is very important to manufacture cabinets in such a manner that either leaks do not occur or, if leaks do occur, they are controlled by preventing contaminated air from entering room air. Prior art cabinets typically had a construction of a box within a box. In some cases, air ducts were bolted onto the side of the cabinets. They were sealed with gaskets. However, no seal is perfect and such construction inherently would present a leak risk.